The latest development comes as Italy ratchets up its operations against people smuggling, aimed at smashing the organised crime ring that has helped more than 250,000 migrants reach Europe from Libya this year.

Calogero Ferrara, the anti-mafia prosecutor placed in command of the operation in Italy, said: “We’ve intercepted thousands of suspicious phone calls between the UK and North Africa, regarding the illegal smuggling of migrants into your country.

The majority of these calls are in Arabic, so it is taking some time to translate them. “However, so far we have whittled that list down to 400 which we believe should be investigated urgently. We believe that most are connected with organised crime, which would fit the pattern elsewhere in Europe.”

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Mr Ferrara confirmed that traffickers were demanding at least £2,000 to smuggle migrants into Britain from France.

Last night a spokesman for the National Crime Agency said: “Though we don’t not discuss operational matters, we do examine all intelligence given to us by partner agencies.

“The NCA has been asked by the Prime Minister to lead a UK law enforcement task force targeting the criminal networks behind people smuggling in the Mediterranean.

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French police stop a migrant from sneaking into lorry

"We are working with agencies in the UK and overseas, utilising the specialist skills of our officers to gather intelligence, identify the criminal groups, pursue them, disrupt their activities, take away their money and their assets, and wherever possible prosecute them.

“An accurate intelligence picture is essential to our investigations. The NCA is providing officers to support the European Joint Operational Team in The Hague and the intelligence cell in Sicily.

“We are deploying officers to support the debriefing of rescued migrants."